The present invention relates to a digital musical instrument with a plurality of musical tone generating circuits for digitally composing digital musical tone data generated from the musical tone generating circuits.
In recent years, electronic musical instruments for generating or forming musical tones using digital technology have been put to practical use. In the instrument of this type having a plurality of musical tone generating circuits for composing the output signals from those circuits, the output signals are passed through a digital to analog (D/A) converter and are mixed in an analog fashion. In the musical tone generating circuit comprises a circuit of the type which generates a single musical tone and a circuit of another type which generates a plurality of musical tones in a time division manner. This type of the musical tone generating circuit needs a plurality of D/A converters, resulting in increase of hardware and manufacturing cost. In this respect, this type of circuit is not best suited for manufacturing compact electronic musical instruments.
For generating a chord in an electronic digital musical instrument, for example a digital electronic keyboard instrument, a sound volume changes in accordance with the number of keys depressed. In an extreme case, a ratio of a single sound to a chord of eight sounds, for example, is 1:8. In expressing the eight times sound volume information in a digital notation, bits for expressing the eight-sound chord are by 3 bits larger than those for the single tone. When the D/A converter of 12 bits is applied for the eight-sound output signal, the single tone is expressed by only the lower 9 bits, and not using the upper three bits. This results in a great deterioration of sound quality.
Conversely, when the single sound is expressed by 12 bits, the digital expression of the chord is necessarily accompanied by an overflow. To avoid this, it is necessary to use a D/A converter for each sound or to use a D/A converter of 15 bits for expressing the chord of 8 sounds.
When the D/A converter is provided for each sound in the digital electronic musical instrument having the plurality of tone generating circuits, the manufacturing cost is increased, the size of the system is increased, and therefore it is impossible to render the musical instrument compact. It is not preferable to use the multibit input D/A converter of 15 bits, for example, for the same reasons that 12 bits (corresponding to 72 dB of the dynamic range) are enough to express musical tone signals of the electronic musical instrument, and the use of the multibit input type D/A converter deteriorates its converting accuracy and increases its manufacturing cost.